1. Field of the Invention
The present invention relates to a device and a method for determining knocking of an internal combustion engine, and particularly to a technique of determining whether knocking has occurred or not based on a waveform of vibration of the internal combustion engine.
2. Description of the Background Art
Various methods have been proposed for determining whether knocking (knock) has occurred or not. Whether knocking has occurred or not is determined, for example, by detecting the magnitude of vibration generated in an internal combustion engine and comparing the magnitude with a threshold value. Meanwhile, in the internal combustion engine, besides vibration due to knocking, vibration could occur when an intake valve or an exhaust valve sits on its seat. Vibration could also occur due to the actuation of an injector (in particular, an in-cylinder direct injector that directly injects fuel into a cylinder) or a high-pressure pump that supplies fuel to the injector. When such vibration due to these factors is detected as noise together with vibration due to knocking, the magnitude of vibration may not be effective at distinguishing vibration due to knocking from the vibration due to noise. Accordingly, a technique has been proposed of determining whether knocking has occurred or not in consideration of both of the magnitude of vibration and the shape of waveform thereof.
Japanese Patent Laying-Open No. 2003-021032 discloses a knock control device for an internal combustion engine using a statistical processing program determining that knocking has occurred upon detecting an output value larger than a knock determination value corrected by statistical processing as well as a waveform shape program using the waveform of vibration for determining whether knocking has occurred or not. The knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2003-021032 includes: a knock sensor detecting knocking in the internal combustion engine; a statistical processing portion statistically processing a signal detected by the knock sensor and input through a low-pass filter and a high-pass filter; a first temporal determination portion determining occurrence of knocking based on a processing result by the statistical processing portion; a second temporal determination portion determining occurrence of knocking based on a waveform shape of the output signal detected by the knock sensor; and a final knock determination portion finally determining occurrence of knocking based on the knock temporal determination of the first temporal determination portion and the knock temporal determination of the second temporal determination portion. When both of the first and second temporal determination portions determine that knocking has occurred, the final knock determination portion finally determines that knocking has occurred. The first temporal determination portion makes a comparison between the maximum value of the output signal detected by the knock sensor and a knock determination value calculated based on the result of processing by the statistical processing portion to determine whether or not knocking has occurred.
According to the knock control device disclosed in the publication, a knock temporal determination by the statistical processing program and a knock temporal determination by the waveform shape program are used, and only when both of the temporal determinations determine that knocking has occurred, it is finally determined that knocking has occurred. As a result, occurrence of knocking can precisely be determined even as to an output signal, which has been erroneously determined by a knock determination employing solely the statistical processing program or the waveform shape program.
The detected vibration of the internal combustion engine includes vibration generated when the intake valve or exhaust valve closes and vibration due to actuation of an injector (in particular, in-cylinder injector for directly injecting fuel into a cylinder) or a fuel pump supplying fuel to the injector, namely includes vibration of the noise component. The magnitude of such vibration is large to the degree that corresponds to the magnitude of vibration generated due to knocking. Therefore, in the case where whether or not knocking has occurred is determined using a maximum value of the output signal detected by the knock sensor as done by the knock control device disclosed in Japanese Patent Laying-Open No. 2003-021032, it could erroneously be determined that knocking has occurred despite the fact that knocking has not actually occurred.